Instrument for measuring rake or hook angle



July 29, 1958 R. w. GRADY 2,844,885

*l INSTRUMENT FOR MEASURING RAKE OR HOOK ANGLE l Filed Aug. l0, 1954 2 Sheets-Sheet 1 IN VEN TOR. ROBERT W. @RALF July 29, 1958 R. w. GRADY A 2,844,885

INSTRUMENT FOR MEASURING RAKE OR HOOK ANGLE l Filed Aug. 10.d 1954 2 Sheets-Sheerl 2 IN V EN TOR. ROBE/P7' W. @IP/712V 2,844,885 Ice Patented July 29, 1958 INSTRUMENT FOR MEASURING RAKE OR HOOK ANGLE This invention relates to an instrument for measuring rake or hook angle, and more particularly to an instrument for determining the rake or hook angle of the cutting faces on the teeth of cutting tools, such as taps, milling cutters, hobs and the like. The device disclosed inthis application constitutes an improvement on the structure disclosed in myv co-pending application Serial No. 404,175, filed January 15, 1954, now Patent No. 2,844,884, issued July 29, 1958, and entitled Instrument for Measuring the Radial Hook or Rake of Taps.

It is well known by those familiar with cutting tools of the above mentioned type, that rake angle refers to the angle of inclination of the cutting faces of the teeth to radial lines through the cutting edges thereof and that this term is generally applied to tools having straight cutting faces. The term hook angle is commonly employed in connection with tools having teeth with concave cutting faces and, with particular reference to taps, refers to the angle formed by a plane extending through the points at the crest and at the roots of the tap teeth with a radial plane through said points at the crests thereof.

In the use of cutting tools of the above mentioned type, the rake or hook angle is determined by the type of material to be cut and varies with the machineability thereof. It is of the utmost importance, and particularly in precision machining operations, that a cutting tool having the proper rake or hook angle be selected for the specic material of the work piece.

Prior to the invention of the device disclosed in my above mentioned patent, the measurement of the rake or hook angle of cutting tools, and particularly of taps, wasa time consuming and tedious operation. My prior device greatly simplified the task of measuring taps, but its use was limited to such tools.

Itis an object of this invention to provide an improved instrument which is particularly useful for measuring the rake or hook angle of taps, but which can also be easily adapted for measuring other cutting tools.

A further object of the invention is to provide a device for the stated purpose in which the cutting tool is manipulated relatively to a stationary magnifying device, as distignuished from my prior structure wherein the magnifying device was moved relatively to thetoo1, in order to greatly facilitate the measurement thereof.

A further object of the instant invention is the provision of an instrument which is highly accurate, durable in construction and which may be easily adapted for use with projection equipment for producing a greatly enlarged image of the cutting teeth on a screen or the like to increase the accuracy of the rake or hook angle measurement.

Further objects and advantages of this invention will be more clearly understood from the following description and from the accompanying drawings in which:

Fig. 1 is a plan view of the instrument embodying my invention.

Fig. 2 is a side view thereof.

Fig. 3 is a fragmentary side view of the device with l parts in central vertical section to more clearly illustrate the construction of the instrument.

Fig. 4 is a fragmentary end view of the front of the instrument with parts removed to more clearly illustrate its construction. I

Fig. 5 is a similar view showing the opposite end of the instrument.

Fig. 6 is a diagrammatic plan view illustrating the first position occupied by a tap whose hook angle is to be determined.

Fig. 7 is a View illustrating the image seen through the microscope of the instrument when the tap is in the position illustrated in Fig. 6.

Fig. 8 is a diagrammatic plan view illustrating the second and third positions occupied by the tap in the process of measuring the hook angle.

Fig. 9 is a View illustrating the images seen through the micros-cope of the instrument when the tap is in the positions illustrated in Fig. 8.

Fig. 10 is a diagrammatic plan view illustrating the final position of the tap.

Fig. 11 is a view of the image seen through 4the miscroscope of the instrument when'the tap is in the iinal position illustrated in Fig. 10.

In the accompanying drawings, I have illustrated the manner in which my improved instrument is constructed and used for measuring the hook angle of a tap in order to more clearly illustrate the advantages of the instrument over that disclosed in my above mentioned patent and also because the primary use of the instrument will be for the measurement of taps since these cutting tools have heretofore proved to be the most difficult to measure. Although I have Iillustrated a tap` having teeth with concave cutting faces and the measurement of the hook angle thereof, it Will be clearly understood from the following description that the rake angle of taps having straight cutting faces can be determined in the same manner .without modification of the instrument.

Referring to the drawings, it will be seen that my instrument includes a base 5 having a ring 6 secured to the, upper surface thereof by screws 7 or the like. Disposed within said ring and extending upwardly therefrom is a circular table 8 which is rotatable relatively to the base 5 and the ring 6 about an axis of rotation extending perpendicularly to said base and indicated at 9. Suitable bear-ing means, not shown, are utilized to rotatably mount the table 8 and said table includes a lower portion S-d and an upper portion 8-b of a smaller diameter providing an annular flange therearound which has an upwardly angled surface containing indicia providing a degree scale 1t) which cooperates with an indicator 11 on the ring 6 to denote the angle through which the table rotates. For the purposes of illustration, it will be said that the table 8 has a normal axis, indicated at 12, which extends diametrically thereacross and intersects its axis of rotation 9 as shown in Fig. l. y

The upper section 8-b of the table 8 contains a dovetailed slot 13 `which extends diametrically thereacross or, as. illustrated in Fig. l, symmetrically with respect to the normal axis 12, and the portions of the table adjacent the opposite edges of the slot 13 are cut away to provide notches 14-14 for the reception of elongated plates 15-15 which are secured to the table by screws 16 and project over the edges of the slot 13 as best illustrated in Figs. 4 and 5.

A carrier member 17 in the form of an elongated block is slidably contained in the slot 13 and is retained therein by the plates 15-15 which engage longitudinally extending shoulders 18--18 on said carrier member. 19 is secured to the rear end of the carrier member 17 by any suitable means and projects upwardly there-` A post.V

. o o 3' fromA between the plates 15'-1S and Vperpendicularly to said carrier member. The opposite' front edges of said' post are bevelled, as at 1941; and it is provided with vertically-.spacedholes.20. l. Y

V l`liet p.supporting, means.` on saidpost 19 include.`

a'supporting'block 21 having. awt-shaped. groove. 21-a in its rear. facewhich cooperates with the bevelled edges ofthepost;.19w tof.position the supporting. block 2'1.

centrally (thereof. Said block is securely vclampedfto.

Vthe.. post. .19 by meansof a .screw 22' which extends Y ingI screw 25 which. extends longitudinally. into the slot 13? andV isA threaded:V into an. elongated threaded hole 26. in the post and the carrier. member .as illustrated in Fig.

y 3. A.yoke 27 is secured to theftable Sadjacent therear rend of the slot 13 and said yoke rotatably supports the.

head 28. of the adjusting: screw.` and retains said screw againstf axial movement..

`In the embodiment of the invention illustrated in the drawings, .the. means for providing an enlarged image ofthe tapteeth'is in theform of a low power, compound.

microscope. of" conventional form whi-chfis slidably carried on a stationary support 30 that is secured to the base. land is adjustable. longitudinally of said. support by meansof .hand wheels 31-31. The microscope contains; fa yconventional lens. system including a transparent member. 3'2 .containing a l hairline 33. and; an eyepiece. 3.4. through which the enlarged image of. the tap teeth is viewed with the. hairline 33 superimposed. thereon.

The optical. axis of the microscope,r which is also the normal axis thereof is indicatedv by thenumeral. 12a andthe hairline'33 is disposed on said optical' axis. and extends. parallel to. the axis of rotation 9. of the'table 8.

When .said table` is in the. fzero position illustrated in Fig.. l, the. optical. axis. 12-a.of the microscope, the hair-V 1ir1ef33, the normal axis 12` of thetableS and the. axis of' 'rotation9. thereoff all lieA inthe same vertical plane. Al-

thoughthe microscope is adjustable along its optical. axis, the. hairline will always remain. in the plane of said axis and parallel to the. axis. of. rotation of the table.

The procedurefor measuring the hookangle ofthe tap illustrated is as follows;

. The supporting block 21y is first located on the post 19 to. support the tap 35. vertically with respect, to the table 8.! T he shank. of. the tap is then. inserted into the V- shapedv groove23 inthe. face of the. block 21 and. under the. spring iinger 24. which. slidably retains the shank in said. groove' andv the. tapis adjusted vertically in the supporting block 21 untill the teeth 36 thereofv are. disposed in the field of vision. of the microscopev 29. The table 8 is then rotated until the proper zero mark on the scale is aligned with,Y the indicator 11 on the ring 6 as illustrated in Fig. l. The microscopev is then adjusted until the image of the tap teeth and. thel-iairline is clearly seen. through the eyepieceY thereof. The tap is then rotated about its own axis 37 in the groove 23 until thevv points 3,8 at'. the crests of the teeth adjacent a flute thereof liealong the. hairline 33. Figv 6 diagrammatically illustrates the position of the tap with respect to the instrument when so adjusted and it will be seen therefrom that theslon'gitudinal axis 37 of the tap, the axis of rotation 9n ofthe table, the 'points 38 and the hairline 33 all lie in the vertical plane of the normal axis 12 and the optical axis' 12-a,. and when viewed through the eyepiece, the points. 38 at the crests of the. tap. teeth willv appearas.

illustrated in'Fig-. 7.` It will be understood that since.- the.VVV

'the longitudinal axis'v 37 of Vthel tap.

, Y v 4 microscope contains a compound lens system, the image seen through the eyepiece is reversed'.

YThe table 8 is then rotated in a counter-clockwise direction, as viewed in Fig. 1, to any desired position which, for the purposes of illustration, will be forty-five degrees. Since the tap is carried by the table 8, it will then assume the. position illustrated in dotted lines in Fig. 8 wherein it will be noted that the normal axis 12 of the t-able is new disposed' angularly' with respect to'l the optical axis 12-a of the microscope, but that the points 38 of thetap teethl stillv lie. in the plane. of saids'normal axis 12 and in alignment with the axis of rotation 9 and through the microscope, the points 38Y atthe crests of the teeth will appear in the position illustrated in dotted lines Y in Fig. 9, or to thev left of the hairline 33.

' The adjusting screw 25 is then rotated in the proper direction to cause. rearward movement of the carrier member 17 inthe slot. 13 which will thereby carry the tapfrearwardly relatively to the.table,.but along the normal axis 12, thereof.. yllhe tap. is viewedv through the microscope. while the adjusting screw is being turned and said tap. is moved -untilv the points 38 at the crests of itsf teeth are again Vbrought into. alignment with the hairline wherein. thetap will then, be located inthe position illustratedl in full lines in.-Figs..8 and 9. It will` be understood from-Figs. 8 and 9, that the points 38 atthe crests. of. the tapfteeth; now lie along the. axis of rotation 9.V of the table 8- sov that upon. rotation of the table in.

either direction, s-aid tap-Will revolve. about an axis extending along. the points 38. The tableis then rotated in. a clockwise direction until the points. at the crests.V of the tapv teeth and the points 38-a. at theroots thereof are. brought into alignment with the hairline. 33 or, asseen through the, microscope, into the position shown in Fig. 11. The tap is now located v as illustrated in. Eig, 10. wherein the points vat the crests and. at'they roots of the vteeth are disposed along the optical axis 12-d. However, the normal axis 12 of ther table. is now angularly disposed with respect to .said opticalaxis. and the, angle a between theaxes 12 and 12-.a and denoted on the'scale 410 is. the hook angle. of the tap.

The. rake. angle of a tap, having straight cutting faces would be obtained. in the same. manner. above. described. Of course the straight. cutting faces of such a tap. would appear as a str-aight. line against the hairline 38 insteadofY thegscalloped. line. Villustrated iny Fig.. l1, which, isa result o f the. concave. faces of the tapshown.

The 'microscope 29 illustrated in the drawings may be replaced by a projection device of any conventional form image of the cutting teeth. on. a. screen or the like to ini; crease the. accuracy ofthe rake. angle measurement.

' It willv be understood thatthe instrument isnot limited tothe-measurement of taps, but. can'. be. applied to circular milling cuttersor other-such. devices by merely modifyingj the tap; supporting means on the post 1.9 tov accommod-ate thev particular cutting, tool. to be measured: and position it'. in sucha manner-that. the cutting edges of, its.

teeth lieparallel tothe axis of rotation-9 of the table. 8.. :Iclaimz-` 1. An'instrumentgfor measuring the rake or hook angle ofl the; teeth: ofja tap, said. instrument including a base, a carrier'. member rotatable relatively to saide base, a post extending perpendicularly from said. carrier member,

. meansfon said postl for supporting saidv tap with thepoints: at"I the. crests. of its teeth'. lying along the axis of rotationof said carrier. member, stationary means ont said base for viewing said teeth and including a. visible reference. line extending. parallel: to said axis of rotation,

and cooperating scale.v and` indicator means on sai-d' car:-

rier member andsaidbase for indicating the angle through which. saidv carrier member. isv turned.

When viewed said post and having a V-shaped notch therein for the reception of the shank of the tap.

3. An instrument for measuring the rake or hook angle of the teeth of a tap, said instrument including a base, a table rotatably mounted on said base and having a normal axis intersecting its axis of rotation, means on said table for supporting a tap with its longitudinal axis intersecting said normal axis and the points at the crests ot its teeth lying along the axis of rotation of said table, stationary means on said base for producing an enlarged image of said teeth and including a visible hairline extending parallel to the said axis of rotation, and cooperative scale and indicator means on said table and said base to indicate the angle through which the table is turned.

4. An instrument for measuring therake or hook angle of the teeth of a tap, said instrument including a base, a table rotatably mounted on said base and having a normal axis intersecting its axis of rotation, means on said table for supporting a tap with its longitudinal axis intersecting said normal axis and lying parallel to said axis of rotation; said tap supporting means being movable relatively to said table and along the normal axis thereof, stationary means on said base for producing an enlarged image of the tap teeth and including a visible hairline extending parallel to the axis of rotation of said table, and a scale on said table cooperating with an indicator on said base to indicate the angle through which the table is turned.

5. An instrument for measuring the rake or hook angle of the teeth of a tap, said instrument including a base, a table rotatably mounted on said base and having a normal axis intersecting its axis of rotation, a carrier member slidably mounted on said table and movable along said normal axis, a post extending perpendicularly from said carrier member, means on said post for supporting a tap with its longitudinal axis intersecting said normal axis and lying parallel to said axis of rotation, a stationary magnifying device on said base for producing an enlarged image of said teeth including a hairline extending parallel to said axis of rotation, and a scale on said table cooperating with an indicator on said base to indicate the angle through which the table is turned.

6. An instrument as set forth in claim 5 wherein there is provided an adjusting screw that is rotatably secured to said table and is threaded into said carrier member to permit adjustment thereof.

7. An instrument for measuring the rake or hook angle of the teeth of a tap, said instrument including a base, a table rotatably mounted on said base and having a normal axis intersecting its axis of rotation and a slot extending thereacross on said normal axis, a carrier member slidable in said slot, an adjusting screw rotatably secured to said table and threaded into said carrier member for moving said carrier member in said slot, a post extending perpendicularly from said carrier member, means on said post for supporting a tap with its longitudinal axis intersecting said normal axis and lying parallel to said axis of rotation, a magnifying device secured to said base for producing an enlarged image of the tap teeth and including a visiblefhairline extending parallel to said axis of rotation; said table having a scale thereon which cooperates with an indicator on said base to denote the angle through which the table is turned.

8. An instrument as set forth in claim 7 wherein the tap supporting means on said post includes a block which extends perpendicularly from the post and has a V- shaped notch in its end portion which is disposed symmetrically with respect to said normal axis of the table and is adapted to receive the shank of a tap.

9. An instrument as set forth in claim 8 wherein said block is adjustable on said post to accommodate taps of diferent lengths.

10. An instrument for measuring the rake or hook angle of a cutting tooth of a cutting tool; said instrument including means providing a normal axis, means for supporting said cutting tool for rotation about an axis of rotation extending along the crest of the tooth to be measured and intersecting said normal axis, stationary means for viewing said tooth including a visible reference line lying in a plane containing said normal axis and said axis of rotation, and cooperating scale and indicator means for indicating the angle through which said cutting tool is revolved relatively to said normal axis.

11. An instrument for measuring the rake or hook angle of a cutting tooth of a cutting tool; said instrument including means providing a normal axis, means for supporting said cutting tool for rotation about its own axis relatively to said supporting means to permit alignment of the crest of the tooth to be measured with a tixed axis extending perpendicularly to and intersecting said normal axis, the said supporting means being adapted for rotating the tool about said fixed axis, and stationary means for viewing said tooth including a visible reference line lying inv a plane containing said normal axis and said fixed axis.

l2. An instrument for measuring the rake or hook angle of a cutting tooth of a cutting tool, said instrument including means providing a normal axis, a rotatable member having an axis of rotation intersecting said normal axis, means on said rotatable member for supporting said cutting tool with the crestof the tooth to be measured lying on said axis of rotation whereby, upon rotation of said rotatable member, said cutting tool revolves about the crest of said tooth, stationary means for viewing said tooth including a visible reference line lying in a plane containing said normal axis and said axis of rotation, and cooperating scale and indicator means for indicating the angle through which said rotatable member is rotated relatively to said normal axis.

13. An instrument for measuring the rake or hook angle of a cutting tool, said instrument including means providing a normal axis, a rotatable member having an axis of rotation intersecting said normal axis, means on said rotatable member for supporting the cutting tool; said supporting means being movable relatively to said rotatable member along said normal axis to permit alignment of the crest of the tooth to be measured with said axis of rotation, stationary means for viewing said tooth including a visible reference line lying in a plane containing said normal axis and said axis of rotation, and cooperating scale and indicator means for indicating the angle through which said rotatable member is turned relatively to said normal axis.

References Cited in the file of this patent -UNTTED STATES PATENTS 199,015 Bausch Ian. 8, 1878 1,424,941 Pirwitz Aug. 8, 1922 1,959,537 Kuhne May 22, 1934 2,420,951 Williams et al. May 20, 1947 2,648,138 Gase Aug. 11, 1953 FOREIGN PATENTS 218,399 Switzerland Apr. 1, 1942 876,855 France Aug. 24, 1942 904,282 France Feb. 19, 1945 994,312 France Aug. 8, 1951 

